This invention relates to a method of testing semiconductor devices using a probe card - a probe test. More particularly, this invention relates to a method of testing semiconductor devices by measuring the maximum variance in distance between the tips of a plurality of needles provided on a probe card and measuring the contact resistance between each needle and the metal film on the corresponding chip area of a semiconductor wafer.
The probe test for checking semiconductor integrated circuit chips (IC chips) which are made on wafers is performed using a probe card with a plurality of needles. In the probe test, a probe with a plurality of needles is disposed above a stage supporting an IC chip thereon.
The tips of the needles are ideally at the same level in height, but actually the level fluctuates somewhat. Where the level fluctuates greatly, the test precision is reduced. For this reason, it is necessary to check the probe card prior to the test. This check is performed using a probe checker. In this case, however, the following problems are raised.
(a) It is necessary to make a periodical check as to whether each needle is at a preset level in the height direction by taking out the probe card.
(b) This check can not be done during the probe test.
(c) The probe checker is expensive, leading to high cost for the measurement.
(d) It is difficult to check the needle level, which requires a precision of several microns, and the contact resistance between each needle and chip area, which is less than 1 (one) ohm.
When measuring the contact resistance between each of the needles provided on a probe card and IC chip supported on a stage, dust is liable to be attached to the tip of needle of the probe card positioned above the state as the needle tip is brought into contact with the IC chip. In such a case, an error is liable to result. To prevent this, the needles are heavily urged against the IC chip by overdriving the stage by a predetermined distance in the same direction after all the needles have been brought into contact with the IC chip.
There are two methods for effecting this.
(a) In one method, the operator observes that all the needles of the probe card are brought into contact with the IC chip area of the wafer, and the stage is raised by a prescribed overdrive extent from that position.
(b) In the other method, the contact of all the needles with the IC chip area is confirmed by a sensor needle, and the stage is raised by an overdrive extent.
The former method, however, requires skill because the check as to whether all the needles are in contact with the wafer is made by naked eyes. Therefore, an error is liable to result depending on the operator, resulting in reduction of the precision of the probe test. In the case of the latter method, damage is liable to be caused to the IC chip by the sensor needle. In addition, the positioning of the needle of the probe and the sensor needle is extremely difficult.